That's interesting - I wonder how this plays out with the strategy for changing to an upfront seat without paying, as mentioned further upthread.
I recently tried it and I indeed got an upfront window seat (I think 4A) in my electronic boarding pass on my flight VIE - ATH. However, at the gate they announced that there was an aircraft change (A321 instead of A320) and therefore lots of people got their seats changed. They also called my name and told me: Sir, there was an aircraft change and we have a new seat for you. Got the new boarding pass that showed.... 4A
And the flight was not full at all...